The invention concerns micro electromechanical switches and more particularly micro electromechanical switch structures.
Micro electromechanical switches are used in a variety of applications up to the microwave frequency range. A micro electromechanical switch is usually a beam with support at one or both ends. The support will normally either extend above a substrate surface or be level with the substrate surface, i.e. a micro electromechanical switch is normally built on top of the substrate surface or into the substrate. The beam acts as one plate of a parallel-plate capacitor. A voltage, known as an actuation voltage, is applied between the beam and an actuation electrode, the other plate, on the switch base. In the switch-closing phase, or ON-state, for a normally open switch, an actuation on voltage exerts an electrostatic force of attraction on the beam large enough to overcome the stiffness of the beam. As a result of the electrostatic force of attraction, the beam deflects and makes a connection with a contact electrode on the switch base, closing the switch. When the actuation on voltage is removed, the beam will return to its natural state, breaking its connection with the contact electrode and opening the switch. A basic micro electromechanical switch is a single pole single throw switch. The beam""s change from open to close or from closed to open is inherently unstable and only controllable up to a certain point. For example, when closing, the beam deforms gradually and predictably, up to a certain point, as a function of the actuation voltage being applied to the switch. Beyond that point, control is lost and the beam""s operation becomes unstable causing the beam to flick down towards the actuation electrode. This behaviour is electrically suitable for simple on/off operation but is usually undesirable if there is a desire to avoid the uncontrollable flick towards the actuation electrode, i.e to control the beam""s movement, and there is therefore room for improvement of micro electromechanical switches.
An object of the invention is to define a manner to control the movement of a beam of a micro electromechanical switch.
Another object of the invention is to define a micro electromechanical switch comprising a beam that is predictably controllable.
A further object of the invention is to define a micro electromechanical continuously variable capacitance.
A still further object of the invention is to define a micro electromechanical power sensor.
Still another object of the invention is to define a micro electromechanical switch with a continuously controllable beam.
Still a further object of the invention is to define a reliable electromechanical switch.
The aforementioned objects are achieved according to the invention by a micro electromechanical switch structure with a continuously controllable beam. The beam is continuously controllable by adding an actuation electrode proximate to, but outside a beam projection. The beam projection is onto and perpendicular to a plane of the actuation electrode. By placing an actuation electrode beside a beam instead of underneath the beam, the actuation electrode can continuously control the movement of the beam from a rest position to a complete actuation.
The aforementioned objects are also achieved according to the invention by a micro electromechanical switching structure comprising a first switching support and a switching beam having a first end and a second end, the first end of the switching beam being supported by the first switching support. According to the invention the micro electromechanical switching structure further comprises a first displaced actuation electrode, spaced apart from a projection of the switching beam, the projection being onto a same plane as the first displaced actuation electrode. This enables a continuous control of the beam gap by applying a continuously variable actuation voltage on the displaced actuation electrode.
The first displaced actuation electrode can in some embodiments be arranged at least partly at the second end of the switching beam. In other embodiments the first displaced actuation electrode can suitably be arranged at least partly parallel to a longitudinal axis of the switching beam. The micro electromechanical switching structure can the suitably further comprise a second displaced actuation electrode arranged substantially in the same plane as the first actuation electrode, spaced apart from the projection of the switching beam, at least in part parallel to a logitudinal axis of the switching beam, and spaced apart from the first actuation electrode by the projection of the switching beam. In some embodiments the micro electromechanical switching structure further comprises a second switching support, the second end of the switching beam being supported by the second switching support, i.e. it is of a bridge type. In other embodiments it can suitably be of a cantilever type.
The micro electromechanical switching structure can suitably further comprise a signal electrode arranged to at least partly coincide with the projection of the switching beam, and/or an actuation electrode arranged to at least partly coincide with the projection of the switching beam, and/or a first capacitor plate arranged on the switching beam of the micro electromechanical switching structure and a second capacitor plate arranged on the base of the micro electromechanical switching structure facing the first capacitor plate.
The aforementioned objects are also achieved according to the invention by a continuously variable capacitor comprising a first connection and a second connection, where the variable capacitor comprises a micro electromechanical switching structure according to any above described embodiment comprising a first and a second capacitor plate and where the first connection is connected to the first capacitor plate and the second connection is connected to the second capacitor plate. In some applications switching beam of the controllable variable capacitor can be offset by biasing the first and/or the second displaced actuation electrode.
The aforementioned objects are also achieved according to the invention by a controllable variable capacitor where the capacitance is controlled by a control voltage. The controllable variable capacitor comprises a continuously variable capacitor according to any above described variable capacitor embodiment where the control voltage is connected to the first and or the second displaced actuation electrode.
The aforementioned objects are also achieved according to the invention by a micro electromechanical switching structure beam measurement device comprising a beam measurement element, included in for example a Wheatstone bridge. The measurement device comprises a first continuously variable capacitor according to any above described embodiment as the beam measurement element, and where a measured beam is the switching beam. The device can in some applications further comprise a second continuously variable capacitor according to any above described embodiment as a reference element of the Wheatstone bridge for the beam measurement element.
The aforementioned objects are also achieved according to the invention by a power measurement unit which measures power flowing through a power signal electrode. The power measurement unit comprises a micro electromechanical switching structure beam measurement device according to any above described embodiment, where the power signal electrode is at least partly arranged under the beam that the micro electromechanical switching structure beam measurement device measures.
By providing a micro electromechanical switching circuit according to the invention a plurality of advantages over prior art micro electromechanical switching circuits are obtained. A primary purpose of the invention is to provide a means to be able to continuously control the beam gap of a micro electromechanical switch element. This is achieved by providing a displaced actuation electrode which is not in any part underneath the beam of a micro electromechanical switch in question. By varying the distance of the displaced actuation electrode from the beam, different control characteristics of the beam gap to displaced actuation electrode voltage can be attained. This will extend the use of micro electromechanical switch elements to analog control and measurement devices such as continuoulsy variable capacitors, both as measurement devices and as a controllable capacitor. The invention is easy to implement and does not need any special manufacturing concerns.
Other advantages of this invention will become apparent from the detailed description.